The present invention relates generally to terminations for connectors and more particularly to connectors having selected impedances that are used in connection with signal cables, such as in an automotive environment.
Many electronic devices rely upon transmission lines to transmit signals between related devices or between peripheral devices and circuit boards of a computer. These transmission lines incorporate signal cables that are capable of high-speed data transmissions.
These signal cables may use what are known as one or more twisted pairs of wires that are twisted together along the length of the cable, with each such twisted pair being encircled by an associated grounding shield. These twisted pairs typically receive complementary signal voltages, i.e., one wire of the pair may see a +1.0 volt signal, while the other wire of the pair may see a −1.0 volt signal. Thus, these wires may be called “differential” pairs, a term that refers to the voltage difference between the two conductors in a signal pair. Such a twisted pair construction minimizes or diminishes any induced noise voltage from other electronic devices and thereby eliminates electromagnetic interference.
As signal cables are routed on a path to an electronic device, they may pass by or near other electronic devices that emit their own electric field. These devices have the potential to create electromagnetic interference to transmission lines such as the aforementioned signal cables. Automotive environments are particularly harsh in electromagnetic interference. Such interference is frequently caused by high voltage ignition signals. Other sources of interference in the automotive environment include alternator charging systems and many switched devices, such as air conditioning. However, this twisted pair construction tends to minimize or diminish any induced electrical fields and thereby substantially eliminates electromagnetic interference.
In order to maintain electrical performance integrity from such a transmission line, or cable, to the circuitry of an associated electronic device, it is desirable to obtain a substantially constant impedance throughout the transmission line, from circuit to circuit or to avoid large discontinuities in the impedance of the transmission line. The difficulty of controlling the impedance of a connector at a connector mating face is well known because the impedance of a conventional connector typically drops through the connector and across the interface of the two mating connector components. Although it is relatively easy to maintain a desired impedance through an electrical transmission line, such as a cable, by maintaining a specific geometry or physical arrangement of the signal conductors and the grounding shield, an impedance discontinuity is usually encountered in the area where a cable is mated to a connector. It is therefore desirable to maintain a desired impedance throughout the connector and its connection to the cable.
Typical signal cable terminations involve the untwisting of the wire pairs and the unbraiding of the braided shield wire and/or foil surrounding the wire pairs. These wires are unbraided manually and this manual operation tends to introduce variability into the electrical performance. This is caused by unbraiding the grounding shield wires, then typically twisting them into a single lead and subsequently welding or soldering the twisted tail of a connector terminal. This unbraiding and twisting often results in moving the signal conductors and grounding shield out of their original state in which they exist in the cable. This rearrangement may lead to a decoupling of the ground and signal wires from their original state that may result in an increase of impedance through the cable-connector junction. Moreover, this twisting introduces mechanical variability into the termination area in that although a cable may contain multiple differential pairs, the length of the unbraided shield wire may vary from pair to pair. This variability and rearrangement changes the physical characteristics of the system in the termination area which may result in an unwanted change (typically an increase) in the impedance of the system in the area.
Additionally, it is common for the signal and ground termination tails of a connector to be arranged into whatever convenient space is present at the connector mounting face without any control of the geometry or spatial aspects of the signal and ground terminals being considered. When signal wires and ground shields are pulled apart from the end of a cable, an interruption of the cable geometry is introduced. It is therefore desirable to maintain this geometry in the termination area between the cable and the cable connector to reduce any substantial impedance increase from occurring due to the cable termination.
The present invention is therefore directed to a terminal contact arrangement and function directed at providing improved connections between connectors and between the mating portions of two interengaging connectors that provides a high level of performance and which maintains the electrical characteristics of the cable in the termination area, particularly in an automotive environment.